In recent years, U.S. carpet manufacturers annually have produced over one billion square yards of carpet. Typically, at least ninety five percent of carpet manufactured in the U.S. is tufted carpet.
A tufted carpet is manufactured by inserting reciprocating needles threaded with a face yarn through a primary carpet backing to form loops or "tufts" of yarn in the primary backing. The tufted primary backing then is washed, dyed if desired, dried and finished. The finishing process typically includes the steps of applying a particulate-filled latex binder to the back of the tufted primary backing to secure the tufts in the primary backing and to adhere a secondary backing to the tufted primary backing.
Primary carpet backings are the foundation of tufted carpet, as the quality, appearance and dimensional stability of tufted carpets depends in large part on the properties of the primary backing. Primary backings can be produced from woven or non-woven materials, and, while both types of materials have advantages, each also has inherent disadvantages.
Woven primary backings can be produced from natural materials such as jute, cotton or kraftcord, or from synthetic materials such as thermoplastic yarns. While woven primary backings are widely used commercially to produce tufted carpet, most woven primary backings can cause tufting needles to deflect during the tufting process, yielding finished carpet that has an uneven or "choppy" appearance. While it is known that needle deflection-related problems in woven backings may be reduced by using flat or fibrillated tape yarns which are more easily split by tufting needles, such yarns typically exhibit reduced tensile strength, especially after being repeatedly pierced during the tufting process. Woven primary backings also often exhibit a tendency to unravel or fray, and have limited dimensional stability because the warp and fill yarns can shift position within the woven material.
Efforts have been made to reduce needle deflection problems in woven primary backings by using lubricants to enhance the ability of needles to penetrate backing yarns. For example, U.S. Pat. No. 3,613,612 teaches the use of 0.2 to 12 weight percent of a tufting needle lubricant on a woven fabric to reduce needle shattering. While the use of such a lubricant may enhance the ability of a needle to penetrate a flat yarn, the lubricant does nothing to prevent fraying or unraveling, and in fact may increase such problems as the lubricant may make it easier for the warp and fill yarns to move relative to one another in the woven material.
Non-woven primary backings typically are spunbonded thermoplastic webs formed from one or more polyesters, polyolefins or combinations of those materials. While nonwoven backing fibers are not susceptible to the unraveling and needle deflection problems noted above, the strength and dimensional stability of such a nonwoven backing deteriorates rapidly as the backing repeatedly is pierced by the tufting needles. Carpets made from non-woven fabrics therefore often have lower tuft retention than carpets made from woven materials. Lower tuft retention means that tufts may be more easily pulled from tufted nonwoven primary backings during the carpet finishing process, yielding carpet that has an uneven finished appearance.
Because both woven and nonwoven carpet backings exhibit undesirable performance characteristics, carpet backing manufacturers have attempted to manufacture improved backings by combining woven backings with supplemental materials to enhance the dimensional stability of woven backings and to reduce fraying of the woven material.
Japanese Laid Open Patent Application No. 62-21862 discloses a primary backing fabric for tufted carpets in which polypropylene tape yarns having concave surface nodes are woven into a fabric which is subsequently laminated to a polypropylene film. While the inventors claim to have produced a backing having improved tuftability and dimensional stability, we believe that polypropylene tape yarn/polypropylene film laminates such as those disclosed in this application cause unacceptably high needle deflection and breakage and that the use of a lamination process prevents such backings from being efficiently produced in large quantities. Therefore, we believe these backings are unsuitable for use in many commercial applications.
U.S. Pat. No. 3,779,799 describes yet another attempt to modify a woven fabric to obtain improved dimensional stability and anti-fray performance. In this patent, a woven material is sprayed or roll-coated with a polymeric substance such as an ethyl vinyl acetate copolymer in an amount of about 0.5 to 0.9 ounces per yard of backing. While the use of the sprayed co-polymer may reduce fraying of the woven material, the drying and curing of the sprayed coating represents a substantial disadvantage when attempting to produce large quantities of such a primary backing. Additionally, sprayed or rolled coatings such as those disclosed in the '799 patent are believed to be incapable of providing backings having sufficient dimensional stability and grab strength for use in demanding applications.
Despite the availability of primary carpet backings such as those described above, the carpet industry continues to demand improved primary backings that are easily tufted, possess high dimensional stability, grab strength and fray resistance, and that can be reliably and easily produced in the large quantities required by carpet manufacturers.